In recent years, there has been a strong request for a reduction of power consumption and quiet operation in a freezing system, such as a freezer-refrigerator for household use, etc. Under such circumstances, use of low-viscosity lubricating oil and reduction of rotational speed of inverter-driven compressors (1200 r.p.m. or so in the case of a refrigerator for household use, for example) are gradually progressing. On the other hand, it is becoming a prerequisite to adopt hydrocarbon based refrigerant, etc. which is a natural refrigerant of low greenhouse coefficient as represented by R134a and R600a, the ozone depleting coefficient of which is zero. Moreover, the conventionally employed method of two-end bearing which supports a shaft at no less than 2 points is effective as element technology for reducing sliding loss and reducing power consumption.
An explanation will be given hereinafter of a conventional hermetic compressor described in Japanese Utility Mode Laid-open No. S52-139407, with reference to drawings.
FIG. 8 is a longitudinal sectional view of a conventional compressor. FIG. 9 is a sectional plan view of a conventional compressor.
In FIG. 8 and FIG. 9, the closed vessel 1 is filled with a refrigerant 2. The electric driving element 5 composed of a stator 3 having a coil portion 3a and a rotor 4, and the compressing element 6 driven by the electric driving element 5 are elastically stored in the vessel 1 by means of suspension spring 7.
The shaft 10 has (i) a spindle portion 11 to which is press fit and fixed the rotor 4, (ii) an eccentric portion 12 formed in eccentricity against the spindle portion 11, (iii) an auxiliary shaft portion 13 provided coaxially with the spindle portion 11, and (iv) a balance weight 10a formed integrally with the shaft 10 between the eccentric portion 12 and the auxiliary shaft portion 13. Furthermore, between the spindle portion 11 and the eccentric portion 12, a joint portion 14 is formed having a diameter smaller than that of the spindle portion 11 and the eccentric portion 12.
The cylinder block 16 has an about cylindrical compression chamber 17, and is provided with a main bearing 18 supporting the spindle portion 11. Over the cylinder block 16, an auxiliary bearing 19 is fixed for supporting the auxiliary shaft portion 13. The piston 20 is inserted, in a way so as to freely slide reciprocatingly, in the compression chamber 17 of the cylinder block 16, and is connected with the eccentric portion 12 through a connecting means 21. The small end portion 21b of the connecting means is connected with the piston 20 by means of a piston pin 22, while the large end portion 21a is connected with the eccentric portion 12.
Now an explanation will be given below of the motions of a hermetic compressor constructed as described above.
The shaft 10 turns with the rotor 4 of the electric driving element 5. As the rotational motion of the eccentric portion 12 is transferred to the piston 20 through the connecting means 21, the piston 20 makes reciprocating motions in the compression chamber 17. With this motion, the refrigerant gas is sucked from the cooling system (not illustrated) into the compression chamber 17 and compressed there, and is then discharged back into the cooling system again.
On the occasion of this compressing action, the reciprocating motion of the piston 20 produces a reciprocating inertial force which is an unbalanced force. This reciprocating inertial force is balanced by a balance weight 10a provided between the eccentric portion 12 and the auxiliary shaft portion 13, in a way so as to be in opposite phase against the piston 20. This offsets to some extent the reciprocating inertial force of the piston 20 in the horizontal direction.
However, with the above-described conventional construction in which a balance weight 10a is provided only on the upper side of the piston 20, although the unbalanced force in the horizontal direction due to reciprocating inertial force of the piston 20 can be offset, an unbalanced force remains in the axial direction of the shaft 10 which is the vertical direction. As a result, this unbalanced force makes the compressing element 6 and the electric driving element 5 vibrate, and this vibration makes the closed vessel 1 vibrate through the suspension spring 7. Namely, the vibrations of the compressor cannot be reduced sufficiently.